In recent years, technological innovation of a display device such as a video display or a projector has enabled higher luminance and higher dynamic range video display than those in a conventional cathode ray tube (CRT) display. While a master monitor (CRT master monitor) in the conventional CRT display has performed display with a luminance of 100 nit (cd/m2) for 100% white of a video signal, for example, the current display device can generally perform display with a luminance of 100 nit or more.
A display device referred to as a High Dynamic Range (HDR) display has also appeared, which can perform display with a luminance of 1000 to 4000 nit.
To perform higher dynamic range video display using the display device such as the HDR display, an HDR EOTF capable of representing an HDR signal range by expanding an Electro-Optical Transfer Function (EOTF) corresponding to a display gamma defined for a conventional Standard Dynamic Range (SDR) display has been required.
As an example of the HDR EOTF, an HDR EOTF to which a Perceptual Quantizer (PQ) having a visually optimum quantization accuracy is applied has been standardized for a display luminance range up to 10000 nit which is wider than a conventional range. The EOTF represented by the PQ is an absolute luminance EOTF because it is defined as a quantization value for an absolute luminance at a video output of the display device.
On the other hand, a characteristic of an image capturing apparatus corresponding to a camera gamma of a video camera generally shows a property, which approximates a reverse characteristic of a display EOTF or to which a total gamma of a system is added, and which is referred to as an Optical-Electro Transfer Function (OETF). The OETF standardized in BT.709 is an SDR OETF optimized for the above described CRT master monitor having a luminance of 100 nit. In recent years, it has been known that a system gamma becomes 1.2 when combined with BT.1886 standardized as an EOTF for a flat panel display.
While the EOTF represented by the PQ is an absolute luminance EOTF, a conventional camera-type OETF is a relative luminance OETF allocated to a sensor output value, which varies depending on dimming using a diaphragm or a filter in a lens optical system, a shutter speed, and a gain setting of a sensor circuit with a sensor output for an object having a standard reflectance as a predetermined reference value. Correct exposure is generally determined with an output value of a standard white object or a 18% gray object as a reference in BT.709, for example.